二元合金等轴枝晶生长相场模拟

在传统纯物质相场模型的基础上，对其中的体系自由能进行重新构造，得到一个紧密联系相图且综合考虑了传热、溶质扩散、界面能各向异性和界面动力学各向异性等适用于二元合金枝晶生长的新相场模型，并利用该模型结合一种能显著提高计算效率的“临界面点相场大梯度计算域控制法”，对AJ-7Si合金在初始过冷度分别为35K和50K的过冷熔体中等轴枝晶生长进行了模拟，得到许多与试验观察相符合的结果；同时在枝晶生长过程中跟踪枝晶主轴尖端，获得其尖端半径和尖端速率，发现随着凝固时间的增加，逐渐收敛，直到枝晶达到稳定生长，而且通过简化KGT模型计算的枝晶尖端的生长速率与模拟值相近。另外，就过冷度对等轴枝晶生长的影响进行了分析。     

A study of the Zn-Rich corner of the Zn-Fe-Sn system

The Zn-rich corner of the 450 °C isothermal section of the Zn-Fe-Sn system was experimentally determined. Within the composition range explored in this study, the liquid phase was found in equilibrium with the ternary extensions of three binary Zn-Fe phases, the ζ, δ, and Γ₁ phases. The ζ phase contains practically no Sn in solid solution; Sn solubility limits in the δ and Γ₁ phases were 2.2 at.% and 7.0 at.%, respectively. The only Fe-Sn compound detected in this study was FeSn, which co-existed with the Γ₁ phase. When its Sn content was lower than approximately 26 at.%, the liquid solidified in water quenching as a degenerated eutectic consisting of a mixture of η-Zn and β-Sn co-existing with primary ζ crystallites. When its Sn content exceeded approximately 70 at.%, the liquid transformed into metallic glass containing mostly Sn, Zn, and a small amount of Fe upon water quenching from 450 °C.     

Influence of particle size on the magnetocaloric and dielectric properties of GdCrO3

Journal of Materials Science: Materials in Electronics - In this paper, the GdCrO3 polycrystalline samples with different particle sizes were prepared by the sol–gel method and the structure,...     

Blocking Ion Migration Stabilizes the High Thermoelectric Performance in Cu2Se Composites

The applications of mixed ionic–electronic conductors are limited due to phase instability under a high direct current and large temperature difference. Here, it is shown that Cu₂Se is stabilized through regulating the behaviors of Cu⁺ ions and electrons in a Schottky heterojunction between the Cu₂Se host matrix and in-situ-formed BiCuSeO nanoparticles. The accumulation of Cu⁺ ions via an ionic capacitive effect at the Schottky junction under the direct current modifies the space-charge distribution in the electric double layer, which blocks the long-range migration of Cu⁺ and produces a drastic reduction of Cu⁺ ion migration by nearly two orders of magnitude. Moreover, this heterojunction impedes electrons transferring from BiCuSeO to Cu₂Se, obstructing the reduction reaction of Cu⁺ into Cu metal at the interface and hence stabilizes the β-Cu₂Se phase. Furthermore, incorporation of BiCuSeO in Cu₂Se optimizes the carrier concentration and intensifies phonon scattering, contributing to the peak figure of merit ZT value of ≈ 2.7 at 973 K and high average ZT value of ≈ 1.5 between 400 and 973 K for the Cu₂Se/BiCuSeO composites. This discovery provides a new avenue for stabilizing mixed ionic–electronic conduction thermoelectrics, and gives fresh insights into controlling ion migration in these ionic-transport-dominated materials.     

SMConf: One-Size-Fit-Bunch,Automated Memory Capacity Configuration for In-Memory Data Analytic Platform

Spark is the most popular in-memory processing framework for big data analytics. Memory is the crucial resource for workloads to achieve performance acceleration on Spark. The extant memory capacity configuration approach in Spark is to statically configure the memory capacity for workloads based on user’s specifications. However, without the deep knowledge of the workload’s system-level characteristics, users in practice often conservatively overestimate the memory utilizations of their workloads and require resource manager to grant more memory share than that they actually need, which leads to the severe waste of memory resources. To address the above issue, SMConf, an automated memory capacity configuration solution for in-memory computing workloads in Spark is proposed. SMConf is designed based on the observation that, though there is not one-size-fit-all proper configuration, the one-size-fit-bunch configuration can be found for in-memory computing workloads. SMConf classifies typical Spark workloads into categories based on metrics across layers of Spark system stack. For each workload category, an individual memory requirement model is learned from the workload’s input data size and the strong-correlated configuration parameters. For an ad-hoc workload, SMConf matches its memory requirement signature to one of the workload categories with small-sized input data and determines its proper memory capacity configuration with the corresponding memory requirement model. Experimental results demonstrate that, compared to the conservative default configuration, SMConf can reduce the memory resource provision to Spark workloads by up to 69% with the slight performance degradation, and reduce the average turnaround time of Spark workloads by up to 55% in the multi-tenant environments.     

Scaling behavior of dynamic hysteresis in multiferroic Bi5FeTi3O15 thin films

Journal of Materials Science: Materials in Electronics - In this study, Bi5FeTi3O15 (BFTO) thin films were obtained on silicon wafers using a sol–gel process. Advanced multiferroic...     

Tubulin Double Helix: Lateral and Longitudinal Curvature Changes of Tubulin Protofilament

By virtue of their native structures, tubulin dimers are protein building blocks that are naturally preprogrammed to assemble into microtubules (MTs), which are cytoskeletal polymers. Here, polycation‐directed (i.e., electrostatically tunable) assembly of tubulins is demonstrated by conformational changes to the tubulin protofilament in longitudinal and lateral directions, creating tubulin double helices and various tubular architectures. Synchrotron small‐angle X‐ray scattering and transmission electron microscopy reveal a remarkable range of nanoscale assembly structures: single‐ and double‐layered double‐helix tubulin tubules. The phase transitions from MTs to the new assemblies are dependent on the size and concentration of polycations. Two characteristic scales that determine the number of observed phases are the size of polycation compared to the size of tubulin (≈4 nm) and to MT diameter (≈25 nm). This work suggests the feasibility of using polycations that have scissor‐ and glue‐like properties to achieve “programmable breakdown” of protein nanotubes, tearing MTs into double‐stranded tubulins and building up previously undiscovered nanostructures. Importantly, a new role of tubulins is defined as 2D shape‐controllable building blocks for supramolecular architectures. These findings provide insight into the design of protein‐based functional materials, for example, as metallization templates for nanoscale electronic devices, molecular screws, and drug delivery vehicles.     

Homogeneity of amorphous solid dispersions – an example with KinetiSol®

KinetiSol^® is a high-shear, fusion-based technology capable of producing stable amorphous solid dispersions (ASDs) without the assistance of solvent. KinetiSol^® has proven successful with multiple challenging BCS class II and IV drugs, where drug properties like thermal instability or lack of appreciable solubility in volatile solvents make hot melt extrusion or spray drying unfeasible. However, there is a necessity to characterize the ASDs like those made by the KinetiSol^® process, in order to better understand whether KinetiSol^® is capable of homogeneously dispersing drug throughout a carrier in a short (<40?s) processing time. Our study utilized the high melting point, BCS class II drug, meloxicam, in order to evaluate the degree of homogeneity of 1, 5, and 10% w/w KinetiSol^®-processed samples. Powder blend homogeneity and content uniformity were evaluated, and all samples demonstrated a meloxicam concentration % relative standard deviation of ≤2.0%. SEM/EDS was utilized to map elemental distribution of the processed samples, which confirmed KinetiSol^®-processed materials were homogeneous at a 25 µm² area. Utilizing Raman spectroscopy, we were able to verify the amorphous content of the processed samples. Finally, we utilized ssNMR ^1?H spin-lattice relaxation measurement to evaluate the molecular miscibility of meloxicam with the polymer at 1% w/w drug load, for the first time, and determined the processed sample was highly miscible at ～200?nm scale. In conclusion, we determined the KinetiSol^® process is capable of producing ASDs that are homogeneously and molecularly well-dispersed drug-in-polymer at drug concentrations as low as 1% w/w.     

Selectivity of multiple-contact nerve cuff electrodes: a simulation analysis

Advances in functional neuromuscular stimulation (FNS) have increased the need for nerve cuff designs that can control multiple motor functions through selective stimulation of selected populations of axons. This selectivity has proved to be difficult to achieve. Recent experiments suggest that it is possible to slowly reshape peripheral nerve without affecting its physiological function. Using computer simulations we have tested the hypothesis that changing the cross section of a nerve from a round to a flat configuration can significantly improve the selectivity of a nerve cuff. We introduce a new index to estimate selectivity to evaluate the various designs. This index is based on the ability of a nerve electrode to stimulate a target axon without stimulating any other axons. The calculations involve a three-dimensional finite element model to represent the electrical properties of the nerve and cuff and the determination of the firing properties of individual axons. The selectivity rating was found to be significantly higher for the Flat Cuff than the Round Cuff. The result was valid with uniform or random distribution of axons and with a random distribution of fascicles diameters. Flattening of individual fascicles also improved the selectivity of the Flat Cuff but only when the number of contacts used was increased to maintain uniform contact density. Therefore, cuff designs that can reshape the nerve into flatter configurations should yield better cuff performance than the cylindrical cuffs but will require higher contact density.